This application is based on an application No. 2000-92385 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an optical pickup that is used to read and write information from and onto an optical recording medium.
2. Related Art
Optical pickups are used when recording/reproducing information for optical recording media such as CDs (compact disks) and DVDs (digital versatile disks). An optical pickup typically includes a movable member and a fixed member. The movable member carries an objective lens for focusing a laser beam onto an optical recording medium, and is made movable so that the objective lens can move in a focusing direction and tracking direction of the optical recording medium. The fixed member supports the movable member. In recent years, a type of optical pickup that has a movable member carrying all optical components of an optical system including an objective lens and a semiconductor laser which emits a laser beam has been proposed (such an optical pickup is hereafter called xe2x80x9coptical-component-integrated optical pickupxe2x80x9d or simply xe2x80x9cintegrated optical pickupxe2x80x9d).
In the optical-component-integrated optical pickup, the entire optical system is mounted in the movable member. When compared with an optical-component-separated optical pickup that mounts the semiconductor laser and the like in the fixed member and moves only the objective lens, the integrated optical pickup does not suffer from degradation in optical properties when the objective lens is moved. Hence stable optical properties can be obtained.
A conventional optical-component-integrated optical pickup is disclosed in Japanese Laid-Open Patent Application No. H07-114743. This optical pickup is provided with an elastic member which allows a movable member to move in a focusing direction, and a means which allows the movable member to rotate in a tracking direction. In this way, the position of the objective lens in the focusing and tracking directions can be adjusted.
In an optical system for recording/reproducing of a high-density optical recording medium such as a DVD, a numerical aperture of an objective lens is generally set large enough to realize high density. This makes it necessary to suppress the amount of tilt of the objective lens relative to the optical recording medium as small as possible. It is therefore desirable to use an actuator that follows the wobbling of the optical recording medium. However, the above conventional optical pickup uses the elastic member such as a flat spring to adjust the position of the objective lens in the focusing direction, thereby making it difficult to adjust the position of the objective lens in the tilting direction.
Also, it is desirable that normal-density optical recording media such as CDs can be reproduced by an apparatus used for recording/reproducing of high-density optical recording media such as DVDs. Furthermore, it is desirable that a plurality of types of optical recording media can be recorded/reproduced by a single optical pickup. Here, a 3-beam method is the most reliable and pervasive tracking error detection method used for reproduction of CDs. Also, a differential push-pull method is used in many optical pickups for recording/reproducing write-once optical recording media such as CD-Rs. Both methods detect a tracking error by focusing three spots of light onto an optical recording medium.
However, the above conventional integrated optical pickup has the following problem. When a tracking error detection method such as the 3-beam method or the differential push-pull method that puts importance on the positional relationship between the spot of light and the track on the optical recording medium is employed in the conventional optical pickup in which the movement of the movable member in the tracking direction is a rotary motion, the positional relationship between the spot and the track constantly changes, which causes variations in amplitude of a tracking error signal.
Also, in an optical-component-integrated optical pickup, the entire optical system is mounted in the movable member. This makes it necessary to install electrical wiring in order to supply drive currents to the semiconductor laser and drive voltages to a photodetector substrate which receives light returning from the optical recording medium, and to send signals detected by the photodetector to a processing circuit equipped in the fixed member. In the aforementioned conventional integrated optical pickup, however, the movable member is connected to the elastic member such as a flat spring to move in the focusing direction, while it is necessary to rotate the movable member in the tracking direction. This being so, even if the member that connects the fixed member and the movable member is conductive, signal lines necessary to exchange electrical signals between the movable member and the outside cannot be secured. Therefore, necessary signal lines have to be secured by using another wiring member such as a flexible printed circuit. This not only increases the number of components, but also tends to cause a problem that signal lines which behave as lines through space affect the properties of the actuator.
Moreover, in an optical pickup provided for high-density optical recording media such as DVDs, the distance from the emission point of the semiconductor laser 113 to the information recording surface of the optical recording medium 107 (such a distance is hereafter called xe2x80x9coverall distancexe2x80x9d) is generally long around 20 mm. Here, the placement of the optical components has to be done such that the beam from the semiconductor laser to the objective lens avoids magnetic circuits used for adjusting the position of the movable member in the focusing and tracking directions. Though it is not unthinkable to provide only one magnetic circuit in the optical pickup, such a construction may give rise to the need to keep the weight balance of the movable member by loading weights or similar into the movable member, which results in an increase of the weight of the movable member.
The object of the present invention is to provide an optical-component-integrated optical pickup that has stable optical properties and is capable of carrying a compact optical system with the overall distance being around 20 mm.
The stated object can be fulfilled by an optical pickup including: a semiconductor laser which emits a laser beam; an objective lens which focuses the emitted laser beam on an optical recording medium; an enclosure which contains an optical system that includes the semiconductor laser and the objective lens; an elastic supporting member which movably supports the enclosure; and a plurality of pairs of driving coils which are contained in the enclosure, each pair being positioned symmetrically with respect to an optical axis of the laser beam, wherein the plurality of pairs of driving coils generate magnetic forces with a plurality of magnets, to drive the objective lens at least in a focusing direction and a tracking direction.
With this construction, an optical pickup with a long overall distance can be realized without increasing a weight of an enclosure which is a movable member.
The object can also be fulfilled by an optical pickup including: a semiconductor laser which emits a laser beam; an objective lens which focuses the emitted laser beam on an optical recording medium; an enclosure which contains an optical system that includes the semiconductor laser and the objective lens; an elastic supporting member which movably supports the enclosure; and a plurality of magnets which are contained in the enclosure and positioned symmetrically with respect to an optical axis of the laser beam, wherein the plurality of magnets generate magnetic forces with a plurality of pairs of driving coils, to generate magnetic fluxes for driving the objective lens at least in a focusing direction and a tracking direction.